Bearing seal with improved contact width

ABSTRACT

A high aspect ratio seal is provided for large roller cone drill bit having a diameter of greater than about 12¼ inches wherein the contact width is narrowed, relative to the width of the seal, to provide a desired contact width.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to earth-boring rotary cone drill bits and in particular to an improved cone seal.

2. Description of Related Art

Earth-boring bits of the type described herein include a bit body having at least one bearing pin, normally three, and a cone rotatably mounted to each bearing pin. Each cone includes cutting elements for engaging the earth formation as the bit body rotates. The bearing spaces between the cavity of the cone and the bearing pin are typically filled with a lubricant.

During typical drilling operations, debris, whether it originates from within the drill bit or from the bore hole, can find its way to the seal and cause wear, which in turn can eventually lead to the failure of the seal. One type of seal includes an elastomeric member having an inner diameter in sliding engagement with the bearing pin and an outer diameter that is normally in static engagement with the cone. These drill bits typically employ either an o-ring seal or a high aspect ratio seal to retain lubricant inside the bearing and to keep drilling fluid and other contaminants out of the bearing. Over time, use can wear down the inner diameter surface of the seal, thereby causing a change in the contact width and the contact pressure of the seal.

One frequent reason for failure of a roller cone drill bit is the wear that occurs on the bearings that support the roller cones. The bearings may be friction-type or roller-type bearings, and the bearings are possibly subjected to high loads, high pressures, high temperatures, and exposure to abrasive particles originating from the formation being drilled. The bearings are typically lubricated with grease that is operable to withstand the conditions encountered during drilling operations. Failure of the seal can ultimately result in failure of the bit, and required retrieval thereof. This may occur before the cutting elements on the cone have worn out, thus prematurely ending the life of the bit.

Roller cone drill bits come in various sizes, typically ranging from as small as 1½ inches in diameter up to 26 inches in diameter, although it is understood these are sizes are merely exemplary and other size roller cone drill bit may be possible. As the size of the drill bit increases, the seal size also increases. The increase in the seal size includes a larger cross section, as well as larger seal inner and outer diameters. Generally, larger drill bits have an increased amount of play or movement of the parts of the drill bit, thus requiring seals of increased depth and width. In large drill bits, defined herein as drill bits having a diameter of greater than about 12¼ inches, the increased seal cross-section provides a substantially larger contact width with the bearing pin and the cone. This increased width reduces or inhibits lubrication of the seal and can accelerate the wear of the seal.

SUMMARY OF THE INVENTION

In this invention, a high aspect ratio seal providing an improved contact width for large drill bits is provided.

In one aspect, a drill bit having a diameter of greater than about 12¼ inches is provided. The bit includes a bit body having a depending bearing pin and a cone having a plurality of cutting elements for engaging a bore hole, wherein the cone includes a cavity that rotatably engages the bearing pin. A groove is formed in the cavity of the cone. The bit includes a ring shaped elastomeric seal in the groove between the bearing pin and the cone. The seal includes an inner diameter surface that sealingly engages the bearing pin, an outer diameter surface that sealingly engages the cone, and two side surfaces. The distance between the inner and outer diameter surfaces defines a radial dimension of the seal and the distance between the side surfaces defines a seal width, wherein the seal has a radial dimension greater than the seal width. An inner diameter contact width is defined as the width of a surface of the inner diameter of the seal that sealingly engages the bearing pin when installed in the drill bit and an outer diameter contact width is defined as the width of a surface of the outer diameter of the seal that sealingly engages the cone when installed in the drill bit. The ratio of the inner diameter contact width (installed) to the seal width (uninstalled) is less than 0.5.

The drill bit may have a diameter greater than about 12¼ inches. In one embodiment, the seal radial dimension is compressed to an amount between about 5 and 15% when installed in the seal groove. In yet other embodiments, the side surfaces comprise at least one protuberance protruding from at least one of the side surfaces of the seal ring for contact with one of the side walls of the groove. In other embodiments, the seal has an inner diameter contact width of between about 0.09 and 0.12 inches, preferably between about 0.1 and 0.11 inches. In other embodiments, the side surfaces are substantially parallel.

In another aspect, at least two drill bits are provided. The first and second drill bits each include a diameter, the second drill bit having a diameter greater than the diameter of the first drill bit, each bit having a bit body that includes a depending bearing pin and a cone that includes a plurality of cutting elements for engaging a bore hole. The cone includes a cavity that rotatably engages the bearing pin, and the cone and the bearing pin include a seal area defined by two annular surfaces, one of which rotates relative to the other. The bits each include an elastomeric seal ring that includes a forward side surface, a rearward side surface and is positioned between the bearing pin and the cone cavity in sealing engagement with the annular surfaces of the seal area. The seal includes an inner diameter surface that contacts the bearing shaft at an inner diameter contact width when installed and an outer diameter surface that contacts the cutter cone at an outer diameter surface contact width when installed, and two side surfaces, wherein the distance between the two side surfaces defines a seal width. The distance between the inner and outer diameter surfaces (uninstalled) of each seal defines a radial dimension of each seal. The radial dimension of the seal of the second drill bit is greater than the radial dimension of the seal of the first drill bit. The inner diameter contact width of the first drill bit and the inner diameter contact width of the second drill bit vary no more than 25% from each other.

In certain embodiments, the second drill bit has a diameter of at least 22 inches. In other embodiments, the inner diameter contact widths of the seals of the first and second drill bits are less than about 0.12 inches. In other embodiments, the inner diameter contact widths of the first and second drill bits are between about 0.09 inches about 0.12 inches, preferably between 0.1 and 0.11 inches. In other embodiments, the seals of the first and second drill bits are compressed to an amount between about 5 and 15% when installed in a seal groove.

In another aspect, a method for designing seals for rotating cone drill bits having diameters in the range from larger than about 12¼ inches to 26 inches is provided. The method includes the steps of: (a) determining a seal width based upon the drill bit diameter, with drill bits of larger diameters in the range having greater seal widths than drill bits of smaller diameters in the range; (b) selecting a seal radial dimension of the seal between the inner and outer diameter surfaces (uninstalled) of the seal to achieve a desired seal squeeze; and (c) configuring the seal such that regardless of the bit diameter in the range and regardless of the seal width selected and seal radial dimension selected, the contact widths are within 33% of each other.

In certain embodiments, step (c) includes making the contact widths less than 0.125 inches. In certain embodiments, step (c) includes making the contact widths between about 0.09 and about 0.12 inches, preferably between about 0.1 and about 0.11 inches. In certain embodiments, the ratio of the inner diameter contact width of the first bit is less than 50% of the seal width of the seal of the first bit. In certain embodiments, step (b) includes selecting a seal squeeze between about 5% and about 15%. In other embodiments, step (b) includes providing greater radial dimensions for seals of larger diameter bits in the range than smaller diameter bits in the range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross sectional view of a roller cone drill bit having a seal in accordance with one embodiment of the invention.

FIG. 2 is a partial cross sectional view of a high aspect ratio seal in accordance with one embodiment of the invention.

FIG. 3 is a cross sectional view of another seal in accordance with one embodiment of the invention.

FIG. 4 is a cross sectional view of another seal in accordance with one embodiment of the invention.

FIG. 5 is a cross sectional view of another seal in accordance with one embodiment of the invention.

FIG. 6 is a cross sectional view of another seal in accordance with one embodiment of the invention.

FIG. 7 is a cross sectional view of another seal in accordance with one embodiment of the invention.

FIG. 8 is a cross sectional view of another seal in accordance with one embodiment of the invention installed in a drill bit.

DETAILED DESCRIPTION

Referring to FIG. 1, the drill bit has a bit body 11 that includes at least one bit leg 13. In certain embodiments, the body 11 includes three bit legs 13. A bearing pin 15 depends downward and forward from each bit leg 13 toward the axis of rotation of the bit. A cone 17 has a cavity 19 that slides over bearing pin 15, allowing cone 17 to rotate relative to bearing pin 15. Cone 17 has a plurality of cutting elements 21 on its exterior. Cutting elements 21 may be tungsten carbide inserts pressed into mating holes, or cutting elements 21 may comprise teeth integrally machined from the body of cone 17. Cone 17 is held on bearing pin 15 by a locking element, which in one embodiment includes a plurality of balls 23 located in mating annular grooves of bearing pin 15 in cone cavity 19.

A lubricant passage 25 extends through each bit leg 13 from a compensator 27 for supplying lubricant to the spaces between the bearing pin 15 and the cavity 19. The lubricant fills the regions adjacent to the bearing surfaces and fills various interconnected passageways. A seal 29 is provided to seal lubricant within the bearing spaces. Compensator 27 reduces the pressure differential across seal 29, which is exposed to borehole pressure on its rearward side and lubricant pressure on its forward side. The bit includes a lubricant reservoir, including a pressure compensator 27 and a lubricant cavity 25, which is connected to the ball passageway by a lubricant passageway. The lubricant is retained in the bearing structure and the various passageways by means of seal assembly 29. Additionally, seal 29 prevents drilled cuttings and drilling fluid from passing the seal and washing out the lubricant and damaging the bearing surfaces.

Most roller cone drill bits having elastomeric seals employ either an o-ring or high aspect ratio seal. A high aspect ratio seal ring has a radial dimension measured from its inner diameter to its outer diameter surface (uninstalled) that is greater than its thickness or width, measured from one side surface to the other side surface. The corresponding seal groove on the roller cone has a depth greater than its width to accommodate the high aspect ratio seal. Sealing engagement occurs between the outer diameter of the seal ring and the groove base and between the inner diameter of the seal ring and the bearing pin. The side surfaces of the seal ring typically do not sealingly engage the side walls of the groove. Normally, the width of the groove is larger than the width of the seal ring so as to allow the seal ring to thermally expand during use, or to allow for the installation of a companion ring.

Lubricants are retained by the seal, which is typically located in the seal groove. The seal can include a static seal surface adapted to form a static seal with the interior surface of the roller cone 17 and a dynamic seal surface adapted to form a dynamic seal with the bearing pin 15 upon which the roller cone is rotatably mounted. The seal is preferably designed to withstand a range of temperature and pressure conditions that the roller cone drill bit will encounter during the operation of the drill bit to prevent lubricants from escaping and/or contaminants from entering the interface between the bearing pin and the cone. Elastomer seals are known in the art and are conventionally formed from a single type of rubber or elastomeric material, and are generally formed having identical configured dynamic and static seal surfaces.

The rubber or elastomeric material selected to form the seal at the interface between the bearing pin 15 and the cone 17 has a specific hardness, modulus of elasticity, wear resistance, and temperature stability, among other properties. The particular geometric configuration of the seal surfaces produces a selected amount of seal deflection that defines the degree of “squeeze” applied by the dynamic and static seal surfaces against respective bearing pin 15 and roller cone surface 17 when the seal is installed in the drill bit. The squeeze may be less than about 20%, preferably between 5 and 15%.

As shown in FIG. 2, a cross-sectional view of one embodiment of seal 29 according to the present invention is provided. Seal 29 has an inner diameter 102, an outer diameter 104, and two substantially parallel side walls 106 and 106′. Seal 29 has a radial dimension 108, defined as the distance to between the point at which inner diameter 102 contacts bearing pin 15 (FIG. 1) and the point at which outer diameter 104 contacts cone 17. Seal 29 also has a seal width 110, defined as the distance between sidewalls 106 and 106′. Referring to FIG. 3, the amount of the surface that inner diameter surface 103 and outer diameter surface 105 that contacts the bearing pin 15 or the cone cavity 19 is defined as the inner diameter seal contact width 112 and outer diameter seal contact width 114, respectively.

Referring now to FIG. 3, one embodiment of seal 29 according to the present invention is provided. Seal 29 includes an inner diameter surface 103, an outer diameter surface 105, and two substantially parallel side walls 106 and 106′. Optionally, side walls 106, 106′ are not substantially parallel. Seal 29 has a radial dimension 108 and a seal width 110, wherein radial dimension 108 is greater than seal width 110. Seal inner diameter surface 103 includes a contact width 112, defined as the portion of the inner diameter surface that sealingly engages the bearing pin when installed and under a specified squeeze. Seal 29 may be installed with a squeeze of less than about 20%. Preferably, seal 29 may be installed with between about 5% to 15% squeeze. The seal outer diameter surface 105 includes a second contact width 114, defined as the portion of the outer diameter surface that sealingly engages a seal groove when installed and under a desired amount of squeeze.

As shown in FIG. 4, in certain embodiments, the inner and outer diameter seal contact widths 112 and 114 are substantially narrower than the seal width 110. Because inner and outer diameter seal contact widths 112, 114 are substantially narrower than the seal width 110, in certain embodiments the seal may include a transition 116 between seal sidewall 106 and seal contact width 112. In certain embodiments, seal transition 116 includes a shoulder between seal sidewall 106 and seal contact width 112. In embodiments wherein the side surfaces are not substantially parallel, the seal width may be defined as the average width of the side surfaces.

The inner diameter contact width 112 may be substantially narrower than the seal width 110, and the outer diameter contact width 114 may be larger than the inner diameter contact width, thereby providing an asymmetric seal.

In certain embodiments, inner and outer diameter seal contact widths 112, 114 are substantially centered about a midline of seal 29, as shown in FIGS. 3-6.

Referring to FIGS. 7A and 7B, two embodiments of seal 29 according to the present invention are provided. Seal 29 includes an inner diameter surface 103, an outer diameter 105 and two side walls, 106 and 106′, which may optionally be substantially parallel. Seal 29 has a radial dimension 108 and seal width 110, wherein the radial dimension is greater than seal width 110. Seal inner diameter surface 103 includes a plurality of contact surfaces 141, 141′ and 141″ that collectively define an inner diameter contact width, which is defined as the portion 142, 142′ and 142″ of each of the contact surfaces that sealingly engages the bearing pin when installed and under a specified squeeze. Contact surfaces 141, 141′, 141″ may be separated by valley 134, 134′. The distance 140 between the outer contact edges 141, 141′, 141″ is substantially less than seal width 110. Seal 29 may be installed with less than 20% squeeze, preferably between about 5% and about 15% squeeze. The seal outer diameter surface 105 includes a plurality of contact surfaces 131, 131′ and 131″ that collectively define an outer diameter contact width, which is defined as the portion 132, 132′ and 132″ of each of the contact surfaces that sealingly engages the seal groove when the seal is installed and under a desired amount of squeeze. Contact surfaces 131, 131′, 131″ may be separated by valley 134, 134′. In certain embodiments, inner diameter contact width, defined as the sum of contact widths 142, 142′, 142″ of contact surfaces 141, 141′, 141″, is between about 0.09 and about 0.12 inches, preferably between 0.1 and 0.11 inches. In certain embodiments, outer diameter contact width, defined as the sum of contact widths 132, 132′, 132″ of contact surfaces 131, 131′, 131″, is between 0.09 and 0.12 inches, preferably between about 0.1 and about 0.11 inches. While the seals provided in FIGS. 7A and 7B are symmetrical, it is understood that in certain embodiments, the seals will not be symmetrical and can include a combination features provided by any of the embodiments provided in FIGS. 3-7.

Inner diameter seal contact width 112 may be arcuate, prior to being installed in the seal groove under a specified squeeze, as shown in FIGS. 3-6. In certain embodiments, outer diameter seal contact width 114 is arcuate, prior to being installed in the seal groove under a specified squeeze, as shown in FIGS. 3-6.

Transition 116 between sidewall 106 and seal contact width 112 may be concave, as shown in FIGS. 3-6. Alternatively, transition 116 between sidewall 106 and seal contact width 112 may be convex (not shown). In certain embodiments, transition 116 between sidewall 106 and seal contact width 112 is linear (not shown). In other embodiments, transition 116 between seal contact width 112 and sidewall 106 maintains a width that is approximately equivalent to seal contact width 112. Optionally, seal contact width 112 remains approximately the same as the seal contact width surface wears and radial dimension 108 of the seal decreases.

In certain embodiments, the slope of transition 116 at the point where seal contact width 112 contacts the transition is substantially parallel to the sidewall 106.

As shown in FIG. 3-5, the width of transition 116 can vary. For example, as shown in FIG. 5, the width of transition 116 can be approximately the same width as the seal contact width 112. Alternatively, the width of transition 116 can be increased substantially, as shown in FIGS. 3 and 4. For example, transition 116 of the seal 29 shown in FIG. 3 includes a slow taper from seal contact width 112 to sidewall 106, whereas the transition of seal 29 shown in FIG. 5 is substantially parallel to the seal sidewalls.

As shown in FIG. 6, seal 29 may include one or more protuberance 120 or stabilizing feature on sidewall 106 of the seal. Alternatively, seal 29 may include at least two protuberances 120 and 120′ located on each of seal sidewalls, 106 and 106′ respectively, as described in U.S. Pub. Patent Application No. 2008/0035382, filed Aug. 14, 2007, claiming priority to U.S. Provisional Application No. 60/837,560, filed Aug. 14, 2006, the disclosures of which are hereby incorporated by reference in their entirety.

FIG. 8 shows one embodiment of the seal of the present invention, when the seal is installed in a drill bit and subjected to a desired amount of squeeze. The drill bit employs a single primary lubricant seal 29. Seal 29 is located within seal groove 31 formed in cone cavity 19. Seal groove 31 is perpendicular to the axis of bearing pin 15 and includes a cylindrical base 34 and substantially parallel flat side walls, which include a forward side surface 36 of the seal groove and a rearward side surface 38 of the seal groove. Cone 17 has a back face 33 that surrounds the mouth of cavity 19. Seal 29 includes an outer diameter 104 and an inner diameter 102. When installed, the surface of the outer diameter 104 contacting the base 34 of the seal groove 31 defines an outer diameter seal contact width 114, and the surface of the inner diameter 102 of the seal 29 contacting the bearing pin 15 defines an inner diameter contact width 112.

Contact width 112 can be between about 0.09 and about 0.12 inches, when installed in the seal groove under a desired amount of squeeze. The contact width, as defined herein, was determined using an Axysymetric FEA model, taking into account the geometry of the gland, the geometry of the seal groove, the modulus of the material used for the seal, and the coefficient of friction for the seal and the contact surfaces. As noted previously, the desired squeeze can be less than about 20%, preferably between 5 and 15%, although it is understood that the squeeze may vary based upon the size and physical properties of the seal. Contact width 112 may be less than about 0.12 inches, when installed in the seal groove under a desired amount of squeeze. In other embodiments, contact width 112 is between about 0.1 and about 0.11 inches, when installed in the seal groove under a desired amount of squeeze.

As shown in Table 1, the contact width can be expressed in terms of a ratio of contact width to seal width, when the seal is installed in the seal groove under a desired amount of squeeze, for large roller cone drill bit. Table 1 shows ratios for various drill bits wherein the contact width is approximately 0.11 inches. The contact width may be about 0.11 inches, and the ratio may be less than about 0.5. In certain embodiments, the ratio can be less than 0.4. In yet other embodiments, the ratio can be less than 0.33.

Table 2 shows ratios for various drill bits wherein the contact width is about 0.1 inches. In certain embodiments wherein the contact width is about 0.1 inches, the ratio is less than 0.44. In other embodiments, the ratio is less than about 0.33. In vet other embodiments, the ratio is less than about 0.29.

TABLE 1 Roller cone drill bit Seal width Contact Ratio of contact diameter (inches) (inches) Width width:seal width 12.25 0.225 0.11 0.49 16 0.295 0.11 0.37 17.5 0.295 0.11 0.37 22 0.34 0.11 0.32 26 0.34 0.11 0.32

TABLE 2 Roller cone drill bit Seal width Contact Ratio of contact diameter (inches) (inches) Width width:seal width 12.25 0.225 0.1 0.44 16 0.295 0.1 0.33 17.5 0.295 0.1 0.33 22 0.34 0.1 0.29 26 0.34 0.1 0.29

When installed in the seal groove, as determined by FEA analysis, certain embodiments of the seal according to the present invention have a contact width substantially less than a typical high aspect ratio seal used in drill bits. For example, a typical high aspect ratio seal for a 16 inch drill bit may have a contact width, when installed and subjected to a squeeze of between about 5% and about 15%, of about 0.125 inches. In contrast, in one embodiment of a seal of the present invention for a 16 inch drill bit, the seal would have a contact width of about 0.110 inches, when installed in the seal groove and subjected to a squeeze of between about 5% and about 15%. Similarly, where as a typical high aspect ratio seal for a 17.5 inch drill bit would have a contact width of about 0.125 inches, when installed in the seal groove and subjected to a squeeze of between about 5% and about 15%, whereas an embodiment of a seal according to one embodiment of the present invention for a 17.5 inch drill bit, when installed in the seal groove and subjected to a squeeze of between about 5% and about 15%, would have a contact width of about 0.105 inches. Finally, a typical high aspect ratio seal for a 22 inch drill bit would have a contact width of about 0.140 inches, when installed in the seal groove and subjected to a squeeze of between about 5% and about 15%, whereas an embodiment of a seal according to one embodiment of the present invention for a 22 inch drill bit, when installed in the seal groove and subjected to a squeeze of between about 5% and about 15%, would have a contact width of about 0.105 inches.

Although the following detailed description contains many specific details for purposes of illustration, one of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope and spirit of the invention. Accordingly, the exemplary embodiments of the invention described herein are set forth without any loss of generality to, and without imposing limitations thereon, the present invention.

As used herein, optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

As used herein, recitation of the term about and approximately with respect to a range of values should be interpreted to include both the upper and lower end of the recited range. Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

As used in the specification and claims, the singular form “a”, “an” and “the” may include plural references, unless the context clearly dictates the singular form.

Although the following detailed description contains many specific details for purposes of illustration, one of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the exemplary embodiments of the invention described below are set forth without any loss of generality to, and without imposing limitations thereon, the claimed invention.

Throughout this application, where patents or publications are referenced, the disclosures of these references in their entireties are intended to be incorporated by reference into this application, in order to more fully describe the state of the art to which the invention pertains, except when these reference contradict the statements made herein. 

1. An drill bit having a diameter of greater than about 12¼ inches, comprising: a bit body having a depending bearing pin; a cone having a plurality of cutting elements for engaging a bore hole, the cone having a cavity that rotatably engages the bearing pin; and a groove formed in the cavity of the cone; a ring shaped elastomeric seal in the groove between the bearing pin and the cone; the seal having an inner diameter that sealingly engages the bearing pin, an outer diameter that sealingly engages the cone, and two side surfaces, the distance between the inner and outer diameter defining a radial dimension of the seal and the distance between the side surfaces defining a seal width, the seal having a radial dimension greater than the seal width; wherein an inner diameter contact width is defined as the width of a surface of the inner diameter of the seal that sealingly engages the bearing pin when installed in the drill bit and an outer diameter contact width is defined as the width of a surface of the outer diameter of the seal that sealingly engages the cone when installed in the drill bit; and wherein the ratio of the installed inner diameter contact width to the uninstalled seal width is less than 0.5.
 2. The drill bit of claim 1 wherein the seal is compressed to an amount between about 5 and 15% when installed in the seal groove.
 3. The drill bit of claim 1 wherein the drill bit has a diameter of at least about 16 inches.
 4. The drill bit of claim 1 wherein the side surfaces comprise at least one protuberance protruding from at least one of the side surfaces of the seal ring for contact with one of the side walls of the groove.
 5. The drill bit of claim 1 wherein the seal has an inner diameter contact width of between about 0.09 and 0.12 inches.
 6. The drill bit of claim 1 wherein the seal has an inner diameter contact width of between about 0.1 and 0.11 inches.
 7. At least two drill bits comprising: first and second drill bits each having a diameter of greater than about 12¼ inches, the second drill bit having a diameter greater than the diameter of the first drill bit, each drill bit comprising; a bit body having a depending bearing pin; a cone having a plurality of cutting elements for engaging a bore hole, the cone having a cavity that rotatably engages the bearing pin, the cone and the bearing pin having a seal area defined by two annular surfaces, one of which rotates relative to the other; an elastomeric seal ring comprising: a forward side surface, a rearward side surface and positioned between the bearing pin and the cone cavity in sealing engagement with the annular surfaces of the seal area; an inner diameter surface contacting the bearing shaft at an inner diameter contact width when installed and an outer diameter surface contacting the cutter cone at an outer diameter surface contact width when installed, and two side surfaces, the distance between the two side surfaces defining a seal width; a radial dimension of each seal defined by the distance between the inner and outer diameter of each seal, the radial dimension of the seal of the second drill bit being greater than the radial dimension of the seal of the first drill bit; and the inner diameter contact width of the first drill bit and the inner diameter contact width of the second drill bit vary no more than 33% from each other.
 8. The drill bits of claim 7 wherein the second drill bit has a diameter of at least 22 inches.
 9. The drill bits of claim 7 wherein the inner diameter contact widths of the seals of the first and second drill bits are each less than about 0.12 inches.
 10. The drill bits of claim 7 wherein the inner diameter contact widths of the first and second drill bits are each between about 0.09 inches and about 0.12 inches.
 11. The drill bits of claim 7 wherein the inner diameter contact widths of the first and second drill bits are each between about 0.1 inches and about 0.11 inches.
 12. The drill bits of claim 7 wherein a ratio of the inner diameter contact width of the first drill bit is less than 50% of the seal width of the seal of the first bit.
 13. The drill bits of claim 7 wherein the seals of the first and second drill bits are each compressed to an amount between about 5 and 15% when installed in a seal groove.
 14. The drill bits of claim 7 wherein the contact widths of the seals of the first and second drill bits are substantially equal.
 15. A method for designing seals for a rotating cone drill bit having a diameter of greater than about 12¼ inches, comprising: (a) determining a seal width based upon the drill bit diameter, with drill bits of larger diameters in the range having greater seal widths than drill bits of smaller diameters in the range; (b) selecting a seal radial dimension of the seal between the inner and outer diameters of the seal to achieve a desired seal squeeze; and (c) configuring the seal for the drill bit such that regardless of the bit diameter in the range and regardless of the seal width selected and seal radial dimension selected, the contact widths for the seals are within 33% of each other for all drill bits in the range.
 16. The method of claim 15 wherein step (c) comprises making the contact widths for the seals less than 0.12 inches.
 17. The method of claim 15 wherein step (c) comprises making the contact widths for the seals between about 0.09 and about 0.12 inches.
 18. The method of claim 15 wherein step (c) comprises making the contact widths for the seals between about 0.1 and about 0.11 inches.
 19. The method of claim 15 wherein a ratio of the inner diameter contact width of a seal is less than 50% of the seal width.
 20. The method of claim 15 wherein step (b) comprises selecting a seal squeeze between about 5% and about 15%.
 21. The method of claim 15 wherein step (b) comprises providing greater radial dimensions for seals of larger diameter bits in the range than for smaller diameter bits in the range. 